Foursquare is pitching that checkin data will be available as targeting markers to advertisers. If advertisers pay for this, they are paying for checkin information.
Take the "soccer moms" example. Foursquare can say "we have X soccer moms checking in." A third party says "Here's an ad we'd like you to serve to soccer moms." Foursquare does it and returns usage data -- how many soccer moms clicked, etc.
Not saying that's how they'd do it, just saying that it's possible, feasible, even easy to provide ad retargeting without any data visibility at all. It's a little early to cry foul, imo.
